1. Field of the Invention
The present invention relates to the field of liquid crystal display, and in particular to a method for saving by-pass capacitor by using circuit board.
2. The Related Arts
A liquid crystal display is a displaying device, which comprise a layer of liquid crystal interposed between two opposite substrates. The displaying device effects light switching by applying electrical excitation and optical anisotropy of the liquid crystal. With the anisotropy of refractivity of liquid crystal molecule, the liquid crystal display applies electrical voltage to the liquid crystal molecule to reorienting the axis of anisotropy of refractivity to control the luminance of light transmitting through the liquid crystal molecule.
FIG. 1 is a schematic view showing the structure of an essential driving circuit for liquid crystal displaying. In the drawing, operation voltages of a source driver 100 and a gate driver 200 are obtained through a DC-DC conversion circuit 300. Since the source driver 100 and the gate driver 200 supply various driving voltages to various pixel units 400 in order to provide the liquid crystal molecules of these pixel units 400 with different rotation angles thereby showing different display grey levels, the voltages on the loads of the source driver 100 and the gate driver 200 are variable with the change of the images. To reduce the influence on the pixel units 400 caused by variation of voltages resulting from loading variation, by-pass capacitors are often connected in parallel to power input terminals of each source driving chip 102 and each gate driving chip 202 in order to stabilize voltage.
As shown in FIGS. 2A and 2B, the operation voltage VDD (3.3V) of the source drivers is obtained from a DC-DC conversion circuit. Each of the source driving chips 102 of the source driver must be connected in parallel with at least one by-pass capacitor C. Similarly, the gate driving chip 202 of the gate driver is also connected in parallel with a plurality of by-pass capacitors C.
For a commonly adopted 1024*768 resolution of a liquid crystal panel, if each source driving chip and gate driving chip is connected in parallel with one single capacitor, then the total number of by-pass capacitors that are connected in parallel to the panel is 786,432. With the size of the liquid crystal panel getting expanded, the corresponding numbers of the source driving chips and gate driving chips used are increased, so that the necessary number of the by-pass capacitors is also increased. This results in an increase of cost and increased complication of circuit.
Further, it is known that a capacitor is made up of two electrode and a dielectric substance interposed therebetween. The dielectric substance is a dielectric medium, which when placed in an electric field between two parallel plate electrodes carrying electrical charges of equal amount but opposite signs, will get polarized so as to form polarization charges on the surfaces of the dielectric medium, causing an increase of the electrical charges bonded on the electrode plates so as to maintain the potential difference between the electrode plates substantially constant, resulting in capacitance effect.